FIG. 16 is a fragmentary cross-sectional view of a known recording magnetic recording head as viewed from a direction parallel to a film thickness direction (Z direction shown in FIG. 16) to a height direction (Y direction shown in FIG. 16).
In FIG. 16, reference numeral 1 represents a return yoke layer, reference numeral 2 represents a main magnetic pole layer, and reference numeral 3 is a sub-yoke layer. As shown in FIG. 16, a front end face 3a of the sub-yoke layer 3 retreats in a height direction (Y direction shown in FIG. 16) from a surface opposed to the recording medium H1a and the main magnetic layer 2 is formed on the sub-yoke layer 3. A front end face 2a of the main magnetic pole layer 2 is exposed from the opposed surface H1a. A nonmagnetic pole gap layer 4 is formed on the main magnetic pole layer 2 and a coil layer 5 is formed on the nonmagnetic pole gap layer 4. A coil insulating layer 6 is formed on the coil layer 5.
The return yoke layer 1 is formed on the coil insulating layer 6. A front end portion 1a of the return yoke layer 1 is opposed to the main magnetic pole layer 2 with the nonmagnetic gap layer 4 interposed therebetween in the opposed surface H1a. A rear end portion 1b of the return yoke layer 1 is magnetically coupled with the main magnetic pole layer 2.
The main magnetic pole layer 2 is formed of a magnetic material having saturation magnetic flux density (Bs) higher than the sub-yoke layer 3. However, since the main magnetic poly layer 2 has low magnetic permeability, the sub-yoke layer 3 formed of a magnetic material having high permeability is overlapped with the main magnetic pole layer 2 and large flux properly leads to the front end portion 2b of the main magnetic pole layer 2. Therefore, it is possible to improve recording efficiency.
As shown in FIG. 16, a flux path leads from the return yoke layer 1 to the main magnetic pole layer 2 at the time of a recording operation. The recording medium M includes a hard film Ma having remanent magnetization thereon and a soft film Mb having high magnetic permeability therein. Magnetic flux φ is concentrated on the front end face 2a of the opposed surface H1a in the main magnetic pole layer 2. The magnetic flux φ leads from the main magnetic pole layer 2 to the return yoke layer 1 via the hard film Ma and the soft film Mb. The hard film Ma is perpendicularly magnetized by the magnetic flux φ. The magnetic data is recorded in the recording medium M.
[Patent Document 1] JP-A-2003-36503 (US2003021063A1)
[Patent Document 2] JP-A-2004-71139 (US2004021985A1)
[Patent Document 3] JP-A-2005-38535 (US2005013044A1)
FIG. 17A is a plan view of the sub-yoke layer 3 and FIG. 17B is a plan view of the main magnetic pole layer 2 overlapped with the sub-yoke layer 3. FIG. 17 shows the magnetic domain structure of the main magnetic pole layer 2 and the sub-yoke layer 3 at the time when current does not flow on the coil layer 5 and a recording magnetic field from the coil layer 5 is not applied to the main magnetic pole layer 2 and the sub-yoke layer 3, that is, at the time of a nonrecording operation. The arrows shown in FIG. 17 represent a spontaneous magnetization direction in each magnetic domain.
As shown in FIG. 17A, the front end face 3a of the sub-yoke layer 3 (X direction shown in FIG. 17A) is formed of an inclined surface inclined in the height direction (Y direction shown in FIG. 17A) toward opposed end faces 3b of the sub-yoke layer 3 approximately from the center of a track width direction (X direction shown in FIG. 17A). For example, an inclination angle θ3 to the track width direction of the front end face 3a (X direction shown in FIG. 17A) is approximately 50 degrees. As shown in FIG. 17, the sub-yoke layer 3 is subjected to multi-magnetic domain states and has magnetic domains 3c. Magnetic domains 3c have a strong component in the height direction (Y direction shown in FIG. 17) of a magnetic moment (or has an only component in the height direction thereof) and occupies a large area in the vicinity of the front end face 3a. 
As shown in FIG. 17B, the main magnetic pole layer 2 includes the elongated front end portion 2b having a track width Tw and a large-width portion 2c formed in the height direction (Y direction shown in FIG. 17B) of the front end portion 2b and has a width in the track width direction (X direction shown in FIG. 17B) larger than the width of the front end portion 2b. The large-width portion 2c shown in FIG. 17B has the same shape as the sub-yoke layer 3 shown in FIG. 17A. As a result, the main magnetic pole layer 2 also is subjected to the multi-magnetic domain state at the time of the nonrecording operation as shown in FIG. 17B.
As shown in FIG. 17B, since the main magnetic pole layer 2 is subjected to the multi-magnetic domain state and has magnetic domains 2d and 2d having the strong component in the height direction (Y direction shown in FIG. 17B) in the vicinity of the front end portion 2b, the front end portion 2b is easily magnetized parallel to the height direction. Therefore, the magnetic flux leaks to the recording medium M from the front end portion 2b at the time of the nonrecording operation, thereby causing the magnetic data recorded in the recording medium M to be erased (Pole Erasure).
Accordingly, the magnetic domain formed on the main magnetic pole layer 2 becomes smaller, thereby reducing the pole erasure.
Since the main magnetic pole layer 2 is overlapped with the sub-yoke layer 3 as shown in FIG. 16, the main magnetic pole layer 2 is affected by the magnetic domain structure of the sub-yoke layer 3, and more particularly, the main magnetic pole layer 2 is strongly affected by the magnetic domain 3c parallel to the height direction in the vicinity of the front end face 3a of the sub-yoke layer 3. Accordingly, the main magnetic pole layer 2 is easily magnetized parallel to the height direction, whereby it is still difficult to properly solve the pole erasure.
The patent documents does not disclose anyway to solve the pole erasure in consideration of the magnetic domain structure of the sub-yoke layer 3 and a position where the main magnetic pole layer 2 overlapped with the sub-yoke layer 3 is formed.